Teaching Thermodynamic, Geometric and Electronic Aspects of Diels-Alder Cycloadditions by Using Computational Chemistry – An Undergraduate Experiment

Abstract

We have applied an undergraduate minicourse of Diels-Alder reaction in Federal University of Rio Grande do Norte. By using computational chemistry tools (Gaussian, Gaussview and Chemcraft) students could build the knowledge by themselves and they could associate important aspects of physical-chemistry with Organic Chemistry. They have performed a very precise G4 method for the quantum calculations in this 15-hour minicourse. Students were taught the basics of Diels-Alder reaction and the influence of frontier orbital theory on kinetics. They learned how to use the quantum chemistry tools and after all calculations they organized and analyzed the results. Afterwards, by means of the PhD student and teacher guidance, students discussed the results and eventually answered the objective and subjective questionnaires to evaluate the minicourse and their learning. We realized that students could understand the influence of substituent effect on the electronic (and kinetic indirectly), geometric and thermodynamic aspects of Diels-Alder reactions. Their results indicated that Diels-Alder reactions are exergonic and exothermic and that although there is an important entropic contribution, there is a linear relation between Gibbs free energy and enthalpy. They learned that electron withdrawing groups in dienophile and electron donating groups in diene favor these reactions kinetically, and on the other hand, the opposite disfavor these reactions. Considering thermodynamically controlled Diels-Alder reactions, the EDG decrease the equilibrium constant, in relation to reference reaction, unlike the EWG. We believe that this minicourse gave an important contribution for Chemistry education at undergraduate level.